Alarm system



Jan. 10, 1956 R. J. MARMoRsToNE 2,730,702

A ALARM SYSTEM Filed Jan. 27, 1953 2 Sheets-Sheet l D- u r c 2 .CT- l N7: o af H CS E f i@ W 5 S N i@ EL .cfr ,N

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EDEPZL :Z MHFmz-'sfmze Milan j VIM/3'2" United States Patent AO ALARMSYSTEM Robert J. Marmorstone, Chicago, Ill., assignor, by mesneassignments, to Panellit, Inc., Skokie, Ill., a corporation of IllinoisApplication January 27, 1953, Serial No. 333,427

9 Claims. (Cl. 340-213) This invention relates to electric alarm systemsfor power plants and the like. It provides particularly a low drain,high versatility, manual reset alarm system.

For reasons of safety which are paramount in an alarm system, and alsofor reasons of economy, such a system should be kept as simple aspossible. Nevertheless it must provide a versatile cycle of alarmoperations in order to distinguish the usual alerting, acknowledge andreset or normal conditions of the plant equipment. Complications havearisen due to the fact that electric energy for the system graduallydrains away, depleting the usual storage battery which should energizethe system to safeguard proper alarm operation even in case of a generalpower failure.

Other complications have been caused by corrosion or electrolyticdecomposition of metallic parts. These difficulties are aggravated whenattempts are made to incorporate a desirably simple system of controlbusses in the circuitry of the system while still providing a versatilecycle of operations.

lt is an object of this invention to overcome these complications andproblems. A particular object is to provide a safe and versatile systemwith zero current drainage through the alarm circuits. A more particularfeature of the new system is that current drainage through a masterrelay is allowed, but allowed only at a rate which is both constant andunobjectionably small. Another particular object is to protect a systemof this type from damage due to corrosion or electrolytic action.

These objects have been achieved, and in particular it has beendiscovered that they are most simply achieved together rather thanindependently, by the use of a new and distinctive system of circuitry,wherein certain elements well known from former alarm arrangements areused in entirely novel positions and for entirely novel functions.

Each alarm signal switch as used in the present system has four basiccircuit systems co-related therewith: a first circuit system for thecontrol of a general, audible annunciator; a second circuit system forthe control of a specific, visual annunciator co-related with the signalswitch; and third and fourth circuit systems controlling respectively afirst and second relay coil. These coils in turn control relay switchesfor the control of the four circuit systems. The coils and switchesmentioned up to this point are installed in relay units or plug-incontainers, one such unit or container being used for each signalswitch. In addition the system requires a single master relay which canserve any number of alarm relay units or plug-in containers. Novelfeatures are provided particularly in the fourth circuit system of eachalarm unit, controlling the second relay coil and in the arrangement ofthe master relay. At these points, special applications of known devicesfor continuity transfer and time delay are provided, thereby allowingwhat is believed to be extreme simplicity for a system of the type asgeneraly described.

Another electric alarm system for a power plant and the like has beendescribed in my co-pending application Serial "ice 2 No. 320,549, filedNovember 14, 1952, now Patent No. 2,709,250; and other electric alarmsystems of the manual reset type have been described in my co-pendingapplications Serial Nos. 316,186, filed October 22, 1952, now Patent No.2,707,777, and 325,393, filed December 11, 1952. Because of theprovision of manual resetting facilities, the present system as well asthose of applications Serial Nos. 316,186 and 325,393 .is somewhat morecornplex than that of application Serial No. 320,549; however, it isbelieved that all of the presently referred to resetting systems areconsiderably simpler than resetting alarm systems heretofore available,and that such simplification has been obtained by novel utilizations ofcontinuity transfer features which heretofore Were used for entirelydifferent alarm purposes. A novel utilization of a continuity transferfeature is also employed in the non-resetting system of applicationSerial No. 320,549.

The specific advantages and features of the new arrangement will beunderstood most clearly upon a study of specific embodiments thereof,shown in the drawing appended hereto and described in the following partof this specification. It should be understood however that a number ofspecific features of said embodiments are subject to considerablechange, within the scope of the claims set forth at the end hereof.

ln the drawing:

Figure l is a schematic diagram of a typical embodiment of thisinvention.

Figure 2 is a schematic diagram of a slightly modified embodiment.

Referring first to Figure l:

The alarm system comprises signal contacts or field switches as shown at11 and 11A. A typical alarm system as contemplated herein comprisesseveral dozens or hundreds or sometimes thousands of such signalcontacts. Each signal contact is normally open in the interest of lowdrain operation. It is closed in predetermined danger situations; forinstance it may be closed by well known thermostatic means, fluid flowresponsive means or equivalent apparatus (not shown).

Such closure of any one signal contact, for instance contact 11, isexpected to excite the alarm system and to cause a general, plantwiseannouncement, such as the sounding of a strong horn 12, in order toalert the plant personnel to the danger. The closure of the switch 11 isexpected simultaneously to cause a more specific announcement, forinstance the lighting up of red and white alarm lamp units 24A and 24AA,associated with the contact 11. This will allow proper supervision ofemergency operations. The lamp units associated with the differentsignal contacts are best installed in a central control room. Theoperations of the annunciators 12, 24A, 24AA are obtained by said firstand second circuit systems and indirectly by said third and fourthcircuit systemsy as will be explained in detail hereinafter` At anysuitable central location, preferably in the same control room, apush-button 15 is provided in order to enable the control room operatoror superintendent to acknowledge and silence the alerting signal soundedby the horn, that is to de-energize the first circuit system. It is alsodesirable, in a versatile alarm installation, to modify the position ofthe second circuit system and the visual alarm caused thereby, forinstance to change it from energization of the red and white light unitsto energization of the red light unit only, by the same operation of theacknowledgment push-button.

When normal conditions are re-established in the field, the signalContact 11 returns to its normal, open position. Ultimately this shouldlead to the turning off of the last alarm lamp; but not at once. Theclosing of the contact 11 was expected automatically to start the alarmcycle; Whereas .the reopening of the contact 11 must not directlyterminate such a cycle,`i`n a manual ieset'system 'as used herein. Sucha manual reset system is frequently preferred, f or instance where theplant operation might be disturbed by indiscriminate restarting of 4the'equipment protected by the alarm system, 'or where it is desired tokeep va detailed log of in service and out 'of service periods for suchequipment. Accordingly the present system provides a reset push-button14 foi the termination of the alarm operation. Depression of thispush-button is eX- pected to open all circuits previously closed,directly or indirectly, by signal switches which are now open. Gn theother hand the push-button 14 must not interfere, practically withcircuits the'sig'nal contacts of which are still closed. To avoid suchinterference has been a problem 'of considerable difficulty in manysystems of this kind. I have discovered however that the object can beachieved very economically and efficiently by a rearrangement of parts,to be described presently, which rearangement also safeguards protectionagainst electrolytic damage in a novel manner. Y

For these'purp'oses the new system Vcomprises an electric storagebattery with a positive terminal P and a negative terminal N; a controlbus C forming a branch of the positive line P and normally disconnectedtherefrom by the acknowledgment switch 15; and another control bus K,forming a branch of the negative line N andnormally connected therewiththrough the reset switch 14. The busses P and C constitute the positiveside while K and N constitute the negative side of the system describedso far. Between these sides a series of alarm relays 17A, 17B, etc. areprovided, one for each signal contact 11, 11A, etc. In addition a masteror reset relay MRI is provided, for the control of the series of alarmrelays 17A, 17B, etc.

The master relay MRI 'has a coil RTD permanently connected between thepositive line P and the control bus K, so that this coil is energized at'all times except during depression of the reset push-button 14. Themaster relay coil RTD controls a normally closed switch RTDI, which dueto the functionally normal energization of the coil RTD is actually openat all times 'except on depression of the reset push-button 14. Inaddition the coil RTD controls a normally open switch RTDZ, which isactually closed at all times except upon depression of push-button 14.Theswitch RTDl is shunted around the acknowledgment push-button 15,being connected between the P and C busses as shown. The switch RTDZ isinterposed on a bus R for the -energization of the annunciator horn 12.The master relay MRI is of the slow operating time delay type. It mayand preferably should be capable of the usual rapid de-energization. Forinstance it may have a time constant of about 18 milliseconds forenergization, causing a corresponding time delay in the opening ofswitch RTDl and closing of switch RTD2. The de- Venergization may occupyabout 10 milliseconds as usual.

Each relay unit 17A, etc. contains two relay coils A and B. Each coil Ais shown as having tive switch units controlled thereby, some of whichare double throw switches and which are identiiied by the symbols A1,A2, A3, A4/A5 and A6/A7. Each coil B is shown with three switch unitsB1, B2/ B3'and B4/B5.

Each relay coil A is controlled by said third circuit system, comprisingin addition to the respective signal contact 11 or 11A, etc., a normallyopen seal-in switch A1 shunted around said contact and therebyconnecting the coil A with the positive terminal P. Each relay'coil B iscontrolled by said fourth circuit system, comprising the continuitytransfer switch B2, B3, which in this system is used mainly for twopurposes: to provide separate-starting'and seal-in circuits for the Bcoil and also to provide a continuity transfer or time delay function,incident to a certain type of energization of the `B coil as will beexplained hereinafter. The normally open pole of the switch B2, B3 isconnected to the positive line `P and the normally closed pole to thebus C. The intermediate pole,

i connected-either with the normally open or the normally closed pole,is connected, through a normally open switch A3, to the B coil, theother end of which is connected to the negative terminal N.

It should be noted that at this point that both coils A and B areconnected permanently to the negative side of the line N. Moreparticularly it is preferred that the negative line N be connected tothe innermost windings of both coils A and B. These precautions placethe positive side P of the line as far as possible from all metal partsof the relay whereon copper might be deposited by any electrolyticcurrents due to moisture in contact with such parts. Preferably thepresence of moisture is also counteracted by hermetically sealing theentire relay unit 17A, 17B, etc., with a dry, neutral gas enclosedtherein. Such double'precaution is desirable for an alarm relay system,where electrolytic decomposition, failure or shorting of any one out ofhundreds of relays could lead to untold harm and damage. Heretofore, ithas not been practical in battery operated alarm systems to connect thenegative side of the line permanently with one end of each alarm coil,and other methods had to be relied upon to counteract ciectrolysis. Thepresent arrangement, with the seal-in switch A2 on the positive side ofthe coil A is usual and mainly with the continuity transfer switch B2,B3 on the positive side of the coil B, simplifies the corrosionprotection of the unit while also simplifying, in a rather unobviousmanner, the safe and eiiicient resetting operation.

Returning now to the description of the first or horn circuit system itwill be noted that this system comprises, in series, a normally openswitch A2 and a normally closed switch B1, interposed between thepositive and horn busses P and R. The second or lamp circuit systemcomprises in parallel two sub-systems. In one of these the red lamp 24Ais connected between the positive or i terminal and two branches,controlled respectively by the normally open and normally closedsides'ALl, A5 of a double throw switch and connected respectively to thenegative or N line and to a testing or T bus, the latter being connectedwith the negative or N line through a normally open push-button 16. Inthe other sub-system the white lamp 24AA is connected between thepositive line and two branches controlled respectively by the open andclosed sides A7, A6 of a double throw switch, the normally closed sidebeing connected to the T bus and the normally open side to another pairof branches. This pairhas normally open and normally closed partsdesignated respectively as B4 and B5 of a further double throw switch,B4 again being connected to the test bus and B5 to the negative bus.

In operation the four circuit systems of each relay 17A, etc. arenormally tie-energized and the signal switch 11 is open. The masterreset coil RTD is energized, Vholding the switch RTD open and RTDZclosed. This yposition of the system is shown in Figure 3.

Closing of the switch 1l causes a first or alerting circuit sequence,the completion of which is shown in Figure l. It comprises (a) closingof a signal circuit P, il, A, K, 14, N, starting energization of coil A;(b) closing of an A coil seal-in circuit P, Ai, A, if., i4, N,continuing such energization even in the case of uctuations between openand closed positions of the signal switch .l1 as frequently encountered;(c) closing of a horn circuit P, A2, Bi, R, RTDZ, i2, N; (d) closing ofa red lamp circuit i?, 24A, A4, N and (e) closing of a white lampcircuit i), MAA, A7, B5, N. in addition a subsequent circuit is preparedby the closing of switch A3. ri`he horn sounds and both the red andwhite lamps are bright.

Depression of the acknowledgment push-button i5 cnergizes the controlbus C thereby causing a second or alarm modifying circuit sequence. itcomprises (a) closing of a coil B starting circuit P, l5, C, B2, A3, B,N; (b) closing of a B coil seal-in circuit i), B3, A3, B, N, wherebycoil B is kept energized even after release of the push-button 15; ("c)opening of vsaid horn circuit, at El 5 and (d) opening of said whitelamp circuit, at B5. The horn stops, the white lamp is extinguished,only the red lamp remains bright.

A return to normal condition, in the equipmentrprotected by the signalswitch 11, opens that switch. lf this happens either during the alertingcondition or during the modified alarm condition of the system itprepares for a resetting but does not effect it. lt only opens thesignal circuit.

The manual resetting of the system, by depression of the push-button 14,inherently occurs either before or after the return to normal and thecorresponding reopening of the switch 11.

lf it occurs after such reopening it causes the following resettingcircuit sequence: (a) opening of the master relay circuit P, RTD, 14,followed by (b) rapid closing of switch RTD1 and rapid opening of switchRTDZ. This is further accompanied by (c) de-energization of the A coilseal-in circuit at 14. This in turn is followed by (d) rapid opening ofthe same circuit at A1; (e) protection of the horn from subsequentenergization by opening of AZ, which permanently inactivates, until thenext alarm, the horn circuit in spite of the immediately followingclosing of the switch B1; (f) de-energization of the coil B at A3; (g)de-energization of the lamp 24A at A4- and (h) de-energization of thelamp 24AA at A7. The de-energization of the coil B also reverses thecontinuity transfer switch B2, B3, thereby re-establishing its normalposition. This operation has no effect upon the other parts, the B coilcircuit being open at A3. Thus the normal de-energization of all fourcircuit systems of the relay unit 17 is re-established. The horn remainssilent and both red and white lamps are now dark. Also all currentdrainage through the relay unit 17 stops. The master relay circuit isrc-established; this is effected by the release of the push-button 14.

If manual resetting is tried tentatively or inadvertently after the endof the alert but before the reopening of the signal switch l1, it causesthe same resetting circuit sequence. In this case however the release ofthe pushbutton la leads to the following further resetting sequence: (i)re-establishment of signal and seal-in circuits for the A coil; (j)re-establishment of the B coil starting circuit. This is achieved inspite of the fact that the acknowledgment push-button 15 at this time isopen. 1t is achieved by the time delay of about 8 milliseconds, causedby the slow operating characteristics of the master relay MRL whichkeeps the shunt switch RTDl closed for a sufficient time to energize thecoil B. This coil again breaks any possible white lamp circuit at B5 andany possible horn circuit at Bl.

A momentary sounding of the horn might be caused in this furtherresetting sequence, by a momentary closed position or" both switches A2and B1, due to slight differences in the energizing speeds of coils Aand B. However even such momentary sounding of the horn is preventedvery simply by the relatively slow reclosing of the switch RTDP.. lnthis manner a very Simple master relay MR is operative not only toprovide basic, distinctive resetting operations but also to avoid eventhe slightest plant disturbance incident to the performance of suchoperations by the simple devices described. It will be noted that thesefeatures are basically achieved oy the cooperation, as described,between the sequence control means or continuity transfer switch B2, B3and the time delay means or relay hlil.

lt remains to note that in an alarm system of this kind. testing of thealarm lamps is important. This can be achieved by depressing the testpush-button 16. Thereupon any re-:i lamps not lighted at such time intheir proper cycle ot operation are energized through the switch A5connected therewith. Any white lamps not lighted at such time in theirproper cycle of operation are then energized through the respectiveswitch A6 or B4.

Further analysis of the system will show that no conf6 fusion, feed-backor the like can be caused even by inadvertent reversals of the sequencein which the operating push-buttons 15 and 14 should be depressed.Likewise, each relay unit 17A, 17B, etc. is independent from operationand possible maintenance operations or the like in other relay units.

Further simplification of each relay unit and lamp system is possible,at the expense of one additional bus wire, by means of a slightlydifferent visual announcing system. This modiied system is shown inFigure 2 and uses an alarm lamp 24 of the back-lighted name plate typewith a flasher arrangement MR2 in the master relay. Back-lighted nameplates and flashers are preferable mainly in two instances: (l) incentral control rooms where there is a great multiplicity of alarms in arelatively small space and where the attendant must read some definitelegend in order to interpret the appearance of an alarm light properly,and (2) in graphic panels where a lettered name plate forms an integralpart of a flow diagram symbol and where the use of more than one lampunit, for the representation of one field apparatus, would be confusing.On the other hand the combination of two light elements of differentcolor as shown in Figure l has the advantage of compactness coupled withexcellent visibility over a wide range of distances and viewing angles,mainly when each lamp is arranged in form of a so-called bullseye unit.When such considerations control the system of Figure l is preferable.

Incidentally it is also possible, so long as all of the bus wires ofFigure 2 are provided, to construct and operate some of the units inaccordance with Figure l and others in accordance with Figure 2. Therewill be no mutual interference or feed-back in that case.

This system provides a flasher relay MR2 the flasher motor of which isconnected in parallel with the horn 12, between the time delay switchRTDZ and the negative line N. The flasher switch of this relay isconnected between the negative side N and the added flasher bus F. Asingle lamp unit 24 is used, which takes the place of the white lampunit 24AA of Figure l and which is similarly connected in principle,except that the switch B4 in this case is not connected to the test busT but to the flasher bus F.

In the operation of this modified system the closing of the signalswitch 11 obviously leads to sounding of the horn and flashing of theback-lighted name plate unit 24. Acknowledgment at 15 lsilences the hornin the same manner as described above and changes the backlighted unit24- frorn flashing to steady illumination. Resetting at 14, subsequentto return to normal conditions at 1l, keeps the horn silent and darkensthe back-lighted name plate unit. This unit can now be tested by thetest button 16. Tentative resetting at 14, prior to the return ofnormalcy at 11, results in the same sequence of protective operationsinvolving the continuity transfer at B2, B3 1n cooperation with the timedelay at RTDI and RTDZ, as described above.

Further modification will become obvious to persons skilled in this art,upon a study of this disclosure.

I claim:

1. A manual reset alarm system for the protection of a series of devicescomprising a source of direct current, positive and negative terminalsconnected with said source, positive and negative control busses,connected with the respective terminals through a normally open and anormally closed push-button switch respectively; a series of alarm relayunits corresponding with -said series of devices and interposed betweensaid positive terminal and control bus on the one hand and said negativeterminal and control bus on the other hand; relay coil and switch meansin cach unit comprising an alarm-modifying coil, a make-before-breakswitch controlled by said coil and connected in series with the positivelside of said coil, and conductors to connect a normally open section ofsaidswitch to a positive terminal, the normally closed section of saidswitch `to the positive control bus, and the other side of said coil tothe negative terminal;a switch shunted around said normally openpush-button switch, and means 'for holding the next to the lastmentioned switch open at all times except upon depression of saidnormally closed push-button switch and for holding said next to the lastmentioned switch closed for a moment following the release of saidnormally closed push-button switch.

2. A low drain alarm system for the protection of a series of devices,comprising a corresponding series of alarm switches; a correspondingseries of alarm relay units; a slow operating master relay associatedwith the entire series of units; at least one annunciator associatedwith each unit; each unit having a rst and a second relay coil and a setof relay switch means controlled thereby and including make-before-breakswitch contacts controlled by at least one of the coils, said relayswitch means being arranged to normally de-energize the respectiveannunciators, to produce a first announcement of the respectiveannunciators while unacknowledged alarm conditions prevail in thecorresponding devices, and to produce a diterent announcement of therespective annunciators while acknowledged alarm conditions prevail inthe corresponding devices; the first coil of each unit being arranged ina circuit with the associated signal switch and being energized throughthe latter signal switch and a seal-in switch controlled by said coil;the second coil of each unit operating said make-before-break switchcontacts and being arranged in an energization circuit for seal-inpurposes extending through a normally open pole of saidmake-before-break switch contacts and, alternatively, for startingpurposes, extending through a trans- 'fer control system in series witha normally closed pole of said make-before-break switch contacts andnormally open contacts controlled by said first coil, said transfercontrol system comprising a normally open manual acknowledgment -switchadapted when closed to energize said second relay coil through saidnormally closed makebefore-break switch contacts and said normally opencontacts of said rst relay coil, said transfer system also including inparallel with said normally open manual acknowledgment switch thefunctionally normally open switch of the Vmaster relay; and amomentarily operable reset switch adapted to momentarily actuate themaster relay and said first coil of each unit, said master relay beingslow operating when returning to its normal condition so that 'saidfunctionally normally open master relay switch remains closed tore-energize said second relayV coil upon release of said reset switch.

3. A system as described in claim 2 additionally comprising a commonalarm annunciator associated with the entire series of units; a commonalarm annunciator energization branch circuit in each of said units, anda pair of series connected switches in each common annunciatorenergi'zation branch circuit, one of said switches in each of saidbranch circuits being a normally open switch controlled by theassociated inst-mentioned coil and vthe other being a normally `closedswitch controlled by the associated second-mentioned coil.

4. A system as described in claim 3 additionally comprising a buscircuit containing said common annunciator, said different commonannunciator branch circuits being branched off from said bus circuit;and a functionally normally'closed switch in said bus circuit controlledby said masterrelay.

"5. A system as described in claim 2 adapted for operation with directcurrent, comprising a positive terminal and a negative terminal, saidrst and second coils of each unit'having a seal-in switch andmake-before-break switch, respectively, interposed between said positiveter- -minaland the coils.

6. A manual reset valarm system for the protection of a series ofdevices comprising apair of energizing voltage terminals, control-bus'es connected with the respective terminals 'through a normally openand a normally closed operable switch respectively; a series of lalarmrelay units corresponding with said series of devices and interposedbetween one of said energizing voltage terminais and one of said controlbuses on the one hand and the other energizing voltage terminal and theother control bus on the other hand; relay coil and switch means in eachunit comprising an alarm modifying coil, a makebefore-break switchcontrolled by said coil and connected i?. series with the side of saidcoil nearest said one energizing voltage terminal, and conductors toconnect a normally closed section of said switch to said one controlbus, a normally closed section of said switch to said one energizingvoltage terminal, and the other side of said coil to said otherenergizing voltage terminal; a switch shunted around said normally openmanually operable switch, and means for holding said next to the lastmentioned switch open at all times except upon opening of said normallyclosed manually operable switch and for holding said next to the lastmentioned switch closed for a moment following the release or closing ofsaid normally closed manually operable switch.

7. A manual reset alarm system for monitoring a series of variablescomprising a pair of energizing voltage termi- `nais, a pair of controlbuses, a series of alarm relay circuits corresponding with said seriesof variables, each of said alarm relay circuits including a pair ofrelays, one of the coils of each circuit connected between one of saidcontrol buses and one of said energizing voltage terminals through acondition responsive signal switch, a slow operating master relayconnected between said one control bus and said one energizing voltageterminal, a normally closed momentarily operable manual reset switchconnected between said one control bus and the other energizingvoltageterminal, the other coil of each circuit connected to saidenergizing voltage terminals through a normally open set of contacts ofthe associated first relay and through a normally open section of amake-beforc-break switch controlled by the associated second relay, eachmake-oetore-break switch having a normally closed section which connectsthe associated coil of the second relay and the normally open set ofcontacts of said first relay tothe other control bus, a normally openmanual acknowledge switch connected between said other control bus andsaid other energizing voltage terminal, whereby depression of saidmanual acknowledgment switch will effect energization of any secondrelay associated with an energized rst relay, whereupon a holdingcircuit is established for the associated second relay through the thenclosed but normally open section of switch, said make-before-break saidmaster relay having a pair of functionally normally open contactsshunting said normally open acknowledgment switch, and said slowoperating master control relay being slow operating when said resetswitch is returned to its normally closed position to rfa-establishenergization of the previously energized second relays, and respectiveannunciator means in each annunciator circuit for providing a rst signal'announcement when the associated first relay coil is energized and theassociated second relay is decnergized, and for providing a secondacknowledged signal announcement when said iirst and second relay coilsare energized.

'3. A manual reset alarm system for monitoring a series of variablescomprising a pair of energizing voltage terminais, a pair of controlbuses, a series of alarm relay circuits corresponding with said seriesof variables, each of said alarm relay circuits including a pair ofrelays, one of the coils of each circuit connected between one of saidcontrol buses and one ot' said energizing voltage terminals through acondition responsive signal switch, the other coil of each circuitconnected to said energizing voltage terminals through a normally openset of contacts of the associated first relay and through a normallyopen section of a make-before-break switch controlled by the associatedsecond relay, each make-before-break switch having a normally closedsection which connects the associated coil of the second relay and thenormally open set of contacts of said first relay to the other controlbus, a normally open manual acknowledge switch connected between saidother control bus and said other energizing voltage terminal, wherebydepression of said manual acknowledgment switch will effect energizationof any second relay associated with an energized first relay, whereupona holding circuit is established for the associated second relay throughthe then closed but normally open section of said make-before-breakswitch, and respective annnnciator means in each annunciator circuit forproviding a rst signal announcement when the associated first relay coilis energized and the associated second relay coil is de-ener gized, andfor providing a second acknowledged signal announcement when said iirstand second relay ooils are energized.

9. A low drain alarm system for the protection of a series of devices,comprising a corresponding series of alarm switches; a correspondingseries of alarm relay units; at least one annunciator associated witheach unit; each unit having a first and second relay coil and a set ofrelay switch means controlled thereby and including makebefore-breakswitch contacts controlled by at least one of the coils, said switchmeans being arranged to normally de-energize the respective annunciator,to produce a iirst announcement of the respective annunciator whileunacknowledged alarm conditions prevail in the corresponding device andto produce a different announcement of the respective annunciate-r whileacknowledged alarm conditions prevail in the corresponding device; theiirst coil of each unit being arranged in a circuit with the associatedsignal switch and being energized through the signal switch; the secondcoil of each unit operating said makebefore-break switch contacts andbeing arranged in an energization circuit for seal-in purposes extendingthrough a normally open pole of said niake-before-break switch andalternatively for starting purposes extending through a transfer controlsystem in series with a normally closed pole or" said makebeforebreakswitch contacts and normally open contacts of said first coil, saidtransfer control system comprising the normally open manualacknowledgment switch. adapted when closed to energize said second relaycoil through said normally closed pole of said make-before-break switch.

References Cited in the tile of this patent UNITED STATES PATENTS1,674,126 Richardson et al June 19, 1928v 1,674,127 Bellamy June 19,1928 2,278,939 Muehter Apr. 7, 1942 2,493,548 Proctor Jan. 3, 19502,600,132 Seaton June l0, 1952

